overcharge

After I came to hellopeter for help about an invoice, Vodacom sorted the problem. I made a payment of R440 in the beginning of Sept after I phoned Vodacom and asked how much I should pay and was told R438 and I paid R440. Now they are billing me again for the month of August together with Sept and I do not understand why as I have been paying every month. I have phoned Vodacom and have been told because of my lines been suspended and have been activated again on the 19th of Aug I am been charged a prorata from 19 Aug untill end of Aug. But it was not my fault my lines were supented. Vodacom made the mistake with the invoice and they suspended my lines because of that. Now that they have sorted out their mistake they credited my account but now sending me an invoice of R900 and my one contract is R349 and the other is R149. Why must I pay R900?I have had so many problems with my account form May when I did my upgrade I am very unhappy!!!!